Botryllus schlosseri (Pallas, 1766)
Botryllus schlosseri is a colonial tunicate that can form colonies as large as 25 mm x 150 mm and up to 2 mm thick. Color is highly variable within and among colonies, and can be yellow, dark purple, red, brown or black. Colonies consist of many radial clusters of 5-20 zooids forming star-shaped systems. Individual zooids can be 1.75 mm - 5 mm long. There are 12-16 oral tentacles around the oral siphon and 7-9 stigmatal rows. The stomach has 8-10 folds and is somewhat spirally deflected with a prominent pyloric caecum. On each side of peribranchial cavity are 1-4 ovaries which are located above prominent testis. Tailed larvae, about 400 µm long, with eight ampullae, may be present in the cavity (Van Name 1945; Nishikawa 1991; Lambert and Lambert 1998). A recent genetic analysis indicates 'Botryllus schlosseri' is probably a complex of cryptic species. Five clades (A-E) were identified in Europe, but only one of these (A) was found at sites in the Northwest Atlantic and Northeast Pacific. The other clades had restricted distributions on the coasts of Europe (Bock et al. 2012). However, Yund et al. (2015) have found that clade A is comprised of several subclades, at least one (BS2) of which is native to the Northwest Atlantic.
possibly native to northeast Pacific
northwest Pacific species, widely introduced